Oil-in-water stable, emulsified spacer fluids

ABSTRACT

Some embodiments described herein provide a method comprising method comprising providing an oil-in-water emulsified spacer fluid comprising a binary surfactant mixture, solvent non-aqueous base fluid, and an aqueous base fluid, wherein the binary surfactant mixture comprises a surfactant and an amphiphilic co-surfactant, wherein the surfactant is present in an amount in the range of from about 0.5% to about 30% by weight of the oil-in-water emulsified spacer fluid and wherein the amphiphilic co-surfactant is present in an amount in the range of from about 0.5% to about 30% by weight of the oil-in-water emulsified spacer fluid, and introducing the oil-in-water emulsified spacer fluid into a subterranean formation comprising a residual non-aqueous fluid therein, wherein the binary surfactant mixture in the oil-in-water emulsified spacer fluid emulsifies at least a portion of the residual non-aqueous fluid.

BACKGROUND

The embodiments herein relate to oil-in-water stable, emulsified spacerfluids for use in subterranean operations.

Subterranean operations (e.g., stimulation operations, sand controloperations, completion operations, etc.) often involve placing a cementcolumn around a casing (or liner) string in a wellbore. The cementcolumn is formed by pumping a cement slurry through the bottom of thecasing and out through an annulus between the outer casing wall and theformation face of the wellbore. The cement slurry develops into a geland then cures in the annular space, thereby forming a column ofhardened cement that, inter alia, supports and positions the casing inthe wellbore and bonds the exterior surface of the casing to thesubterranean formation. Among other things, the cement column may keepfresh water zones from becoming contaminated with produced fluids fromwithin the wellbore. The cement column may also prevent unstableformations from caving in, thereby reducing the chance of a stuck drillpipe or a casing collapse. Additionally, the cement column forms a solidbarrier to prevent fluid loss or contamination of production zones. Thedegree of success of subterranean operation involving placement of acement column depends, therefore, at least in part, upon the successfulcementing of the wellbore casing.

In order to effectively cement wellbore casing, adequate displacement oftreatment fluids previously introduced into the wellbore (collectivelyreferred to herein as “pre-cement treatment fluids”), particularly thosecomprising natural or synthetic oils (e.g., drilling fluids), isessential. This is because many pre-cement treatment fluids,particularly oleaginous fluids, tend to be incompatible with the cementcuring processes. For this reason, adequate displacement of pre-cementtreatment fluids is essential to achieve strong bonding between thecement and the subterranean formation and the cement and the casing(i.e., in the annulus between the outer casing wall and the formationface), to realize proper zonal isolation, structural integrity of thecement column, and the like. Traditionally, optimal removal ofpre-cement treatment fluids prior to a cementing operation employs theuse of spacer fluids formulated to have specific properties (e.g.,plastic viscosity, yield point, density, and the like) depending ondownhole requirements. As used herein, the term “spacer fluid” and allof its variants (e.g., “spacer”) refers to any fluid used to physicallyseparate one fluid from another.

Generally, surfactant additives are included in spacer fluids ascleaning agents to both aid in displacing the pre-cement treatmentfluids and to water-wet the face of the subterranean formation and/orthe casing. As used herein, the term “water-wet” refers to dispositionof a film of aqueous fluid (e.g., water) coating on a surface (e.g., theface of a subterranean formation or the surface of casing). Surfactantsalone may poorly emulsify and/or excessively foam, thereby decreasingthe effectiveness of the surfactant to remove a pre-cement treatmentfluid. Surfactants may additionally remain in the subterranean formationwhere they contaminate the cement in cementing operations, ofteninterfering with the mechanical properties of the cement and, thus, acement column's integrity. That is, while surfactants are useful inremoving pre-cement treatment fluids and in preparing the surfaces, theymay be detrimental to the cement if left behind, particularly in largequantities.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of theembodiments disclosed herein, and should not be viewed as exclusiveembodiments. The subject matter disclosed is capable of considerablemodifications, alterations, combinations, and equivalents in form andfunction, as will occur to those skilled in the art and having thebenefit of this disclosure.

FIG. 1 depicts an embodiment of a system configured for delivering theoil-in-water emulsified spacer fluids of the embodiments describedherein to a downhole location.

DETAILED DESCRIPTION

The embodiments herein relate to oil-in-water stable, emulsified spacerfluids for use in subterranean operations. Specifically, the embodimentsdisclosed herein relate to micro-, mini-, and macro-stable emulsifiedspacer fluids comprising a binary surfactant mixture, a non-aqueous basefluid, and an aqueous base fluid. The binary surfactant mixture maycomprise lipophilic and/or hydrophilic domains that may be capable ofemulsifying, or incorporating, non-aqueous fluids into the emulsifiedspacer fluid. Thus, the emulsified spacer fluid may be used to remove atleast a portion of a non-aqueous fluid from a subterranean formation.

The binary surfactant mixture of the emulsified spacer fluids may alsoincrease the water wettability of a subterranean formation. As usedherein, the term “water wettability” and all of its variants (e.g.,“water wet”) refers to adhesion of an aqueous fluid to the surface of asubterranean formation. The productivity of hydrocarbon producingsubterranean formations, for example, may be improved if the formationis water wet, as a thin film of aqueous fluid may coat the surface ofthe formation and increase oil transport efficiency.

The emulsified spacer fluids described herein are stable emulsions. Asused herein, the term “stable emulsion” and all of its variants refersto an emulsion having droplets that do not generally coalesce (i.e.,combine to form larger droplets), flocculate (i.e., aggregate together),or cream (i.e., rise to the top of the emulsion) at a particulartemperature and/or pressure. As used herein, the term “droplet” refersto an isolated fluid phase having a specific shape, which may be anyshape including, but not limited to, a cylindrical shape, a sphericalshape, a tubular shape, an irregular shape, and the like, and anycombination thereof. Thus, the oil-in-water emulsified spacer fluidsdescribed herein may be characterized as having relatively evenlydispersed droplets therein.

The oil-in-water emulsified spacer fluids disclosed herein may comprisea binary surfactant mixture, a non-aqueous base fluid, and an aqueousbase fluid, forming a three-phase micro-, mini-, and macro-stableemulsion. Such three-phase emulsions may form a Winsor emulsion. Thereare four general Winsor-type emulsions. In a Winsor-type I emulsion, thesurfactant or binary surfactant mixture, such as that disclosed herein,forms an oil-in-water emulsion in the aqueous base fluid phase. In aWinsor-type II emulsion, the surfactant or binary surfactant mixture, asdescribed in some embodiments herein, forms a water-in-oil emulsion inthe non-aqueous base fluid phase. In a Winsor-type III emulsion, thesurfactant or binary surfactant mixture, as described herein, forms anemulsion in a separate phase between the aqueous base fluid phase andthe non-aqueous base fluid phase. Finally, in Winsor-type IV emulsion,the surfactant or binary surfactant mixture, such as that disclosedherein, the aqueous-based fluid, and the non-aqueous based fluid areequally solubilized, such that a single-phase emulsion is formed.

The oil-in-water emulsified spacer fluids described herein may becharacterized thermodynamically stable, optically transparent ortranslucent, dilutable in aqueous base fluids, as defined herein,capable of increasing water wettability of surfaces, and emulsifying, orincorporating therein, non-aqueous fluids. In addition, the oil-in-wateremulsified spacer fluids may have a relatively low viscosity, increasingthe pumping efficiency during subterranean operations.

Although some embodiments described herein are illustrated by referenceto cementing operations in subterranean formations, the emulsifiedspacer fluids may be used in any subterranean operation that may benefitfrom having non-aqueous fluids removed therefrom and/or increased waterwettability. Such treatment operations may include, but are not limitedto, a drilling operation; a lost circulation operation; a stimulationoperation; an acidizing operation; an acid-fracturing operation; a sandcontrol operation; a completion operation; a scale inhibiting operation;a water-blocking operation; a clay stabilizer operation; a fracturingoperation; a frac-packing operation; a gravel packing operation; awellbore strengthening operation; a sag control operation; and anycombination thereof. Moreover, the emulsified spacer fluids describedherein may be used in any non-subterranean operation that may benefitfrom its non-aqueous fluid removal and/or water wetting qualities. Suchoperations may be performed in any industry including, but not limitedto, oil and gas, mining, chemical, pulp and paper, converting,aerospace, medical, automotive, and the like.

One or more illustrative embodiments disclosed herein are presentedbelow. Not all features of an actual implementation are described orshown in this application for the sake of clarity. It is understood thatin the development of an actual embodiment incorporating the embodimentsdisclosed herein, numerous implementation-specific decisions must bemade to achieve the developer's goals, such as compliance withsystem-related, business-related, government-related, and otherconstraints, which vary by implementation and from time to time. While adeveloper's efforts might be mixture and time-consuming, such effortswould be, nevertheless, a routine undertaking for those of ordinaryskill the art having benefit of this disclosure.

It should be noted that when “about” is provided herein at the beginningof a numerical list, the term modifies each number of the numericallist. In some numerical listings of ranges, some lower limits listed maybe greater than some upper limits listed. One skilled in the art willrecognize that the selected subset will require the selection of anupper limit in excess of the selected lower limit. Unless otherwiseindicated, all numbers expressing quantities of ingredients, propertiessuch as molecular weight, reaction conditions, and so forth used in thepresent specification and associated claims are to be understood asbeing modified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by theexemplary embodiments described herein. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claim, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques.

While compositions and methods are described herein in terms of“comprising” various components or steps, the compositions and methodscan also “consist essentially of” or “consist of” the various componentsand steps. When “comprising” is used in a claim, it is open-ended.

In some embodiments, an oil-in-water emulsified spacer fluid isdescribed herein comprising a binary surfactant mixture, a non-aqueousbase fluid, and an aqueous base fluid. In some embodiments, a method oftreating a subterranean formation is provided comprising introducing theoil-in-water emulsified spacer fluid into the subterranean formation,wherein the binary surfactant mixture emulsifies, or incorporates, atleast a portion of residual non-aqueous fluid within the subterraneanformation. As such, removal of the oil-in-water emulsified spacer fluidfrom the subterranean formation also removes at least a portion of theresidual non-aqueous fluid within the subterranean formation. In someembodiments, the oil-in-water emulsified spacer fluid may be introducedafter a wellbore is drilled into the subterranean formation, removed,and then followed by a cementing operation comprising introducing acasing string into the subterranean formation and introducing a cementcomposition into the subterranean formation so as to form a cementcolumn in an annulus between the subterranean formation and the casingstring.

The binary surfactant mixture in the oil-in-water emulsified spacerfluids disclosed herein may comprise a surfactant and an amphiphilicco-surfactant. The surfactant may be used to form an interfacial film onthe non-aqueous base fluid dispersed phase in the emulsified spacerfluid and the co-surfactant may be used to ensure flexibility of theinterfacial film, thus reducing interfacial tension and aiding thestability of the emulsion. Additionally, the binary surfactant mixtureis capable of increasing the water wettability of a subterraneanformation and other surfaces that contact the emulsified spacer fluid.

Suitable surfactants for use in the binary surfactant mixture mayinclude, but are not limited to, anionic surfactant; a cationicsurfactant; a zwitterionic surfactant; and any combination thereof.Specific examples of suitable surfactants may include, but are notlimited to, a betaine; a sulfated alkoxylate; a sulfonated alkoxylate;an alkyl quaternary amine; an alkoxylated linear alcohol; an alkylsulfonate; an alkyl aryl sulfonate; C₁₀-C₂₀ alkyldiphenyl ethersulfonate; a polyethylene glycol; an ether of alkylated phenol; a sodiumdodecylsulfate; an alpha olefin sulfonate (e.g., sodium dodecanesulfonate, trimethyl hexadecyl ammonium bromide, and the like); anarginine methyl ester; an alkanolamine; an alkylenediamide; an alkylester sulfonate; an alkyl ether sulfonate; an alkyl ether sulfate; analkali metal alkyl sulfate; a sulfosuccinate; an alkyl disulfonate; analky aryl disulfonate; an alkyl disulfate; an alcohol polypropoxylatedsulfate; an alcohol polyethoxylated sulfate; a taurate; an amine oxide;an alkylamine oxides; an ethoxylated amide; an alkoxylated fatty acid;an alkoxylated alcohol; an ethoxylated fatty amine; an ethoxylated alkylamine; an alkylaminobetaine; a quaternary ammonium compound; anyderivative thereof; and any combination thereof.

Suitable amphiphilic co-surfactants for use in the embodiments disclosedherein may include, but are not limited to, an alcohol; an alkylalcohol; an aliphatic alcohol; an alicyclic alcohol; an unsaturatedaliphatic alcohol; an unsaturated alicyclic alcohol; a polyhydricalcohol; an aromatic alcohol; an ethoxylated alcohol; a propoxylatedalcohol; a glycol; a glycol ether; a polyglycol amine; a phenol; anethoxylated phenol; a propoxylated phenol; and any combination thereof.Specific examples of suitable amphiphilic co-surfactants include, butare not limited to, methanol; ethanol; n-propanol; isopropanol;n-butanol; sec-butanol; isobutanol; t-butanol; benzyl alcohol;cyclohexanol; 2-ethyl hexanol; amine ethyl ethanolamine;cyclohexylamine; diethanolamine; diethylamine; diethylenetriamine;diethylethanolamine; di-isopropanolamine; di-isopropylamine;dimethylethanolamine; ethylene diamine; isopropylamine;monoethanolamine; monoisopropanolamine; morpholine; triethanolamine;triethylamine; tri-isopropanolamine; diethylene glycol; dipropyleneglycol; ethylene glycol; polyethylene glycol; tripropylene glycol;triethylene glycol; propylene glycol; polypropylene glycol; polyglycol;hexylene glycol; glycerine; nonylphenol; nonylphenol ethoxylate;nonylphenol polyethylene; nonylphenol polyethylene ether; nonylphenoxypoly(ethyleneoxy)ethanol; tertiary-butyl alcohol; any derivativethereof; and any combination thereof.

In some embodiments, the surfactant may be present in an amount in therange of from a lower limit of about 0.5%, 1%, 2.5%, 5%, 7.5%, and 10%,12.5%, and 15% to an upper limit of about 30%, 27.5%, 25%, 22.5%, 20%,17.5%, and 15% by weight of the emulsified spacer fluid and theamphiphilic co-surfactant may be present in an amount in the range offrom a lower limit of about 0.5%, 1%, 2.5%, 5%, 7.5%, 10%, 12.5%, and15% to an upper limit of about 30%, 27.5%, 25%, 22.5%, 20%, 17.5%, and15% by weight of the emulsified spacer fluid having no additivesincluded therein. In some embodiments, the surfactant to amphiphilicco-surfactant ratio may be in the range of from an upper limit of about3:1, 2.8:1, 2.6:1, 2.4:1, 2.2:1, and 2:1 to a lower limit of about 1:1,1.2:1, 1.4:1, 1.6:1, 1.8:1, and 2:1. In exemplary embodiments, thesurfactant to amphiphilic co-surfactant ratio may be 2:1.

The oil-in-water emulsified spacer fluids described herein may be amicro-, mini-, or macro-stable emulsion. As used herein, the term“microemulsion” refers to a stable, isotropic emulsion comprisingdispersed phase droplets with an average diameter in the range of from alower limit of about 1 nm, 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm to anupper limit of about 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, and 50 nm. Insome embodiments, the dispersed phase droplets in the microemulsion havean average diameter in the range of from a lower limit of about 10 nm,12.5 nm, 15 nm, 17.5 nm, 20 nm, 22.5 nm, 25 nm, 27.5 nm, and 30 nm to anupper limit of about 50 nm, 47.5 nm, 45 nm, 42.5 nm, 40 nm, 37.5 nm, 35nm, 32.5 nm, and 30 nm. As used herein, the term “miniemulsion” refersto a stable emulsion comprising dispersed phase droplets with an averagediameter in the range of from a lower limit of about 50 nm, 100 nm, 150nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, and 500 nm to anupper limit of about 1 μm, 950 nm, 900 nm, 850 nm, 800 nm, 750 nm, 700nm, 650 nm, 600 nm, 550 nm, and 500 nm. As used herein, the term“macroemulsion” refers to a stable emulsion having comprising dispersedphase droplets with an average diameter of greater than about 0.1 μm. Insome embodiments, the macroemulsion comprises dispersed phase dropletshaving an average diameter in the range of from a lower limit of about 1μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, and 50μm to an upper limit of about 100 μm, 95 μm, 90 μm, 85 μm, 80 μm, 75 μm,70 μm, 65 μm, 60 μm, 55 μm, and 50 μm. In exemplary embodiments, whereoil-in-water emulsified spacer fluids disclosed herein aremacroemulsions, a low-molecular weight surfactant is selected for use inthe binary surfactant mixture so as to prevent or reduce any coalescenceof the dispersed phase droplets. Additionally, the macroemulsion may befurther stabilized by Pickering stabilization, characterized by includedin the oil-in-water emulsified spacer fluid inert solids that arecapable of adsorbing onto the interface between the dispersed phasedroplets and the continuous phase (e.g., silica, carbon black, bariumsulfate, calcium carbonate, clay, and the like).

The non-aqueous base fluid in the oil-in-water emulsified spacer fluidsmay be any water-insoluble liquid that is capable of forming a stableemulsion with the aqueous base fluids and binary surfactant mixturesdisclosed herein. Suitable non-aqueous base fluids may include, but arenot limited to, an alkane; a cyclic alkane; an olefin; an aromaticorganic compound; an aliphatic organic compound; a paraffin; a diesel; amineral oil; a synthetic oil; a desulfurized hydrogenated kerosene; andany combination thereof. In some embodiments, the non-aqueous base fluidmay be present in the oil-in-water emulsified spacer fluids in an amountin the range of from a lower limit of about 1%, 2.5%, 5%, 7.5%, 10%,12.5%, 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, and 30% to an upper limit ofabout 60%, 57.5%, 55%, 52.5%, 50%, 47.5%, 45%, 42.5%, 40%, 37.5%, 35%,32.5%, and 30% by weight of the emulsified spacer fluid having noadditives included therein.

The aqueous base fluid for use in the oil-in-water emulsified spacerfluids may include, but is not limited to, fresh water; saltwater (e.g.,water containing one or more salts dissolved therein); brine (e.g.,saturated salt water); seawater; and any combination thereof. Generally,the aqueous base fluid may be from any source, provided that it does notcontain components that may adversely affect the stability and/orperformance of the oil-in-water emulsified spacer fluids describedherein. In some embodiments, the aqueous base fluid may be present inthe oil-in-water emulsified spacer fluids in an amount in the range offrom a lower limit of about 40%, 42.5%, 45%, 47.5%, 50%, 52.7%, 55%,57.5%, 60%, 62.5%, 65%, 67.5%, and 70% to an upper limit of about 98%,95%, 92.5%, 90%, 87.5%, 85%, 82.5%, 80%, 77.5%, 75%, 72.5%, and 70% byweight of the emulsified spacer fluid having no additives includedtherein.

In some embodiments, the oil-in-water emulsified spacer fluids mayfurther comprise an additive so as to improve the stability of theemulsion, render the emulsified spacer fluid more effective atperforming a particular subterranean operation, to effectively addresscertain qualities of the subterranean formation (e.g., permeability,propensity for fines formation, and the like), and the like. Suitableadditives that may be used in the oil-in-water emulsified spacer fluidsdescribed herein include, but are not limited to, a salt; a weightingagent; an inert solid; a fluid loss control agent; an emulsifier; adispersion aid; a corrosion inhibitor; an emulsion thinner; an emulsionthickener; a viscosifying agent; a gelling agent; a proppant; a lostcirculation agent; a foaming agent; a gas; a pH control additive; abreaker; a biocide; a crosslinker; a stabilizer; a chelating agent; ascale inhibitor; a gas hydrate inhibitor; an oxidizer; a reducer; afriction reducer; a clay stabilizing agent; and any combination thereof.

In various embodiments, systems configured for delivering theoil-in-water emulsified spacer fluids described herein to a downholelocation are described. In various embodiments, the systems can comprisea pump fluidly coupled to a tubular, the tubular containing theoil-in-water emulsified spacer fluids.

The pump may be a high pressure pump in some embodiments. As usedherein, the term “high pressure pump” will refer to a pump that iscapable of delivering a fluid downhole at a pressure of about 1000 psior greater. A high pressure pump may be used when it is desired tointroduce the oil-in-water emulsified spacer fluids to a subterraneanformation at or above a fracture gradient of the subterranean formation,but it may also be used in cases where fracturing is not desired. Insome embodiments, the high pressure pump may be capable of fluidlyconveying particulate matter, such as proppant particulates, into thesubterranean formation. Suitable high pressure pumps will be known toone having ordinary skill in the art and may include, but are notlimited to, floating piston pumps and positive displacement pumps.

In other embodiments, the pump may be a low pressure pump. As usedherein, the term “low pressure pump” will refer to a pump that operatesat a pressure of about 1000 psi or less. In some embodiments, a lowpressure pump may be fluidly coupled to a high pressure pump that isfluidly coupled to the tubular. That is, in such embodiments, the lowpressure pump may be configured to convey the oil-in-water emulsifiedspacer fluids to the high pressure pump. In such embodiments, the lowpressure pump may “step up” the pressure of the oil-in-water emulsifiedspacer fluid before it reaches the high pressure pump.

In some embodiments, the systems described herein can further comprise amixing tank that is upstream of the pump and in which the oil-in-wateremulsified spacer fluid is formulated. In various embodiments, the pump(e.g., a low pressure pump, a high pressure pump, or a combinationthereof) may convey the oil-in-water emulsified spacer fluid from themixing tank or other source of the oil-in-water emulsified spacer fluidto the tubular. In other embodiments, however, the oil-in-wateremulsified spacer fluid can be formulated offsite and transported to aworksite, in which case the oil-in-water emulsified spacer fluid may beintroduced to the tubular via the pump directly from its shippingcontainer (e.g., a truck, a railcar, a barge, or the like) or from atransport pipeline. In either case, the oil-in-water emulsified spacerfluid may be drawn into the pump, elevated to an appropriate pressure,and then introduced into the tubular for delivery downhole.

FIG. 1 shows an illustrative schematic of a system that can deliveroil-in-water emulsified spacer fluids of the embodiments describedherein to a downhole location, according to one or more embodiments. Itshould be noted that while FIG. 1 generally depicts a land-based system,it is to be recognized that like systems may be operated in subsealocations as well. As depicted in FIG. 1, system 1 may include mixingtank 10, in which an oil-in-water emulsified spacer fluid of theembodiments disclosed herein may be formulated. The oil-in-wateremulsified spacer fluid may be conveyed via line 12 to wellhead 14,where the oil-in-water emulsified spacer fluid enters tubular 16,tubular 16 extending from wellhead 14 into subterranean formation 18.Upon being ejected from tubular 16, the oil-in-water emulsified spacerfluid may subsequently penetrate into subterranean formation 18. Pump 20may be configured to raise the pressure of the oil-in-water emulsifiedspacer fluid to a desired degree before its introduction into tubular16. It is to be recognized that system 1 is merely exemplary in natureand various additional components may be present that have notnecessarily been depicted in FIG. 1 in the interest of clarity.Non-limiting additional components that may be present include, but arenot limited to, supply hoppers, valves, condensers, adapters, joints,gauges, sensors, compressors, pressure controllers, pressure sensors,flow rate controllers, flow rate sensors, temperature sensors, and thelike.

Although not depicted in FIG. 1, the oil-in-water emulsified spacerfluid may, in some embodiments, flow back to wellhead 14 and exitsubterranean formation 18. In some embodiments, the oil-in-wateremulsified spacer fluid that has flowed back to wellhead 14 maysubsequently be recovered and recirculated to subterranean formation 18.

It is also to be recognized that the disclosed oil-in-water emulsifiedspacer fluids may also directly or indirectly affect the variousdownhole equipment and tools that may come into contact with theoil-in-water emulsified spacer fluids during operation. Such equipmentand tools may include, but are not limited to, wellbore casing, wellboreliner, completion string, insert strings, drill string, coiled tubing,slickline, wireline, drill pipe, drill collars, mud motors, downholemotors and/or pumps, surface-mounted motors and/or pumps, centralizers,turbolizers, scratchers, floats (e.g., shoes, collars, valves, etc.),logging tools and related telemetry equipment, actuators (e.g.,electromechanical devices, hydromechanical devices, etc.), slidingsleeves, production sleeves, plugs, screens, filters, flow controldevices (e.g., inflow control devices, autonomous inflow controldevices, outflow control devices, etc.), couplings (e.g.,electro-hydraulic wet connect, dry connect, inductive coupler, etc.),control lines (e.g., electrical, fiber optic, hydraulic, etc.),surveillance lines, drill bits and reamers, sensors or distributedsensors, downhole heat exchangers, valves and corresponding actuationdevices, tool seals, packers, cement plugs, bridge plugs, and otherwellbore isolation devices, or components, and the like. Any of thesecomponents may be included in the systems generally described above anddepicted in FIG. 1.

Embodiments disclosed herein include:

A. A method comprising: providing an oil-in-water emulsified spacerfluid comprising a binary surfactant mixture, solvent non-aqueous basefluid, and an aqueous base fluid, wherein the binary surfactant mixturecomprises a surfactant and an amphiphilic co-surfactant, wherein thesurfactant is present in an amount in the range of from about 0.5% toabout 30% by weight of the oil-in-water emulsified spacer fluid andwherein the amphiphilic co-surfactant is present in an amount in therange of from about 0.5% to about 30% by weight of the oil-in-wateremulsified spacer fluid, and wherein the amphiphilic co-surfactant isselected from the group consisting of an alcohol; an alkyl alcohol; analiphatic alcohol; an alicyclic alcohol; an unsaturated aliphaticalcohol; an unsaturated alicyclic alcohol; a polyhydric alcohol; anaromatic alcohol; an ethoxylated alcohol; a propoxylated alcohol; aglycol; a glycol ether; a polyglycol amine; a phenol; an ethoxylatedphenol; a propoxylated phenol; and any combination thereof; andintroducing the oil-in-water emulsified spacer fluid into a subterraneanformation comprising a residual non-aqueous fluid therein, wherein thebinary surfactant mixture in the oil-in-water emulsified spacer fluidemulsifies at least a portion of the residual non-aqueous fluid.

B. An oil-in-water emulsified spacer fluid comprising: a binarysurfactant mixture, solvent non-aqueous base fluid, and an aqueous basefluid, wherein the binary surfactant mixture comprises a surfactant andan amphiphilic co-surfactant, wherein the surfactant is present in anamount in the range of from about 0.5% to about 30% by weight of theemulsified spacer fluid and wherein the amphiphilic co-surfactant ispresent in an amount in the range of from about 0.5% to about 30% byweight of the emulsified spacer fluid, and wherein the amphiphilicco-surfactant is selected from the group consisting of an alcohol; analkyl alcohol; an aliphatic alcohol; an alicyclic alcohol; anunsaturated aliphatic alcohol; an unsaturated alicyclic alcohol; apolyhydric alcohol; an aromatic alcohol; an ethoxylated alcohol; apropoxylated alcohol; a glycol; a glycol ether; a polyglycol amine; aphenol; an ethoxylated phenol; a propoxylated phenol; and anycombination thereof.

Each of embodiments A and B may have one or more of the followingadditional elements in any combination:

Element 1: Wherein the binary surfactant mixture increases the waterwettability of the subterranean formation.

Element 2: Wherein oil-in-water emulsified spacer fluid is amicroemulsion comprising dispersed phase droplets having an averagediameter in the range of from about 1 nm to about 100 nm.

Element 3: Wherein the oil-in-water emulsified spacer fluid is aminiemulsion comprising dispersed phase droplets having an averagediameter in the range of from about 50 nm to about 1 μm.

Element 4: Wherein the oil-in-water emulsified spacer fluid is amacroemulsion comprising dispersed phase droplets having an averagediameter in the range of from about 1 μm to about 100 μm.

Element 5: Wherein the surfactant is selected from the group consistingof an anionic surfactant; a cationic surfactant; a zwitterionicsurfactant; and any combination thereof.

Element 6: Wherein the non-aqueous base fluid is selected from the groupconsisting of an alkane; a cyclic alkane; an olefin; an aromatic organiccompound; an aliphatic organic compound; a paraffin; a diesel; a mineraloil; a synthetic oil; a desulfurized hydrogenated kerosene; and anycombination thereof.

Element 7: Wherein the surfactant is selected from the group consistingof a betaine; a sulfated alkoxylate; a sulfonated alkoxylate; an alkylquaternary amine; an alkoxylated linear alcohol; an alkyl sulfonate; analkyl aryl sulfonate; C₁₀-C₂₀ alkyldiphenyl ether sulfonate; apolyethylene glycol; an ether of alkylated phenol; a sodiumdodecylsulfate; an alpha olefin sulfonate; an arginine methyl ester; analkanolamine; an alkylenediamide; an alkyl ester sulfonate; an alkylether sulfonate; an alkyl ether sulfate; an alkali metal alkyl sulfate;a sulfosuccinate; an alkyl disulfonate; an alky aryl disulfonate; analkyl disulfate; an alcohol polypropoxylated sulfate; an alcoholpolyethoxylated sulfate; a taurate; an amine oxide; an alkylamineoxides; an ethoxylated amide; an alkoxylated fatty acid; an alkoxylatedalcohol; an ethoxylated fatty amine; an ethoxylated alkyl amine; analkylaminobetaine; a quaternary ammonium compound; any derivativethereof; and any combination thereof.

Element 8: Wherein the emulsified spacer fluid further comprises anadditive selected from the group consisting of a salt; a weightingagent; an inert solid; a fluid loss control agent; an emulsifier; adispersion aid; a corrosion inhibitor; an emulsion thinner; an emulsionthickener; a viscosifying agent; a gelling agent; a proppant; a lostcirculation agent; a foaming agent; a gas; a pH control additive; abreaker; a biocide; a crosslinker; a stabilizer; a chelating agent; ascale inhibitor; a gas hydrate inhibitor; an oxidizer; a reducer; afriction reducer; a clay stabilizing agent; and any combination thereof.

Element 9: Removing the oil-in-water emulsified spacer fluid from thesubterranean formation; introducing a casing string into thesubterranean formation; introducing a cement composition into thesubterranean formation so as to form a cement column in an annulusbetween the subterranean formation and the casing string; and settingthe cement composition forming the cement column.

Element 10: Wherein the binary surfactant mixture is capable ofemulsifying at least a portion of a non-aqueous fluid.

By way of non-limiting example, exemplary combinations applicable to Aand B include: A with 1, 3, and 6; A with 4, 7, and 9; B with 1, 2, and8; and B with 5, 7, and 10.

To facilitate a better understanding of the embodiments describedherein, the following examples of preferred or representativeembodiments are given. In no way should the following examples be readto limit, or to define, the scope of the disclosure.

Example 1

In this example, the stability of the oil-in-water emulsified spacerfluids described herein comprising various amounts of solventnon-aqueous base fluid was evaluated. A 14-ppg non-emulsified controlspacer fluid was prepared comprising 51.5% by weight of the controlspacer fluid of barite (weighting agent) and 5% by weight of the controlspacer fluid of a mixture comprising 25% by weight of betaine(surfactant) and 25% by weight of tertiary-butyl alcohol (co-surfactant)in fresh water (aqueous base fluid) to balance. Three experimental14-ppg oil-in-water emulsified spacer fluids were prepared. The firstoil-in-water emulsified spacer fluid (TF1) was prepared using 51.2% byweight of TF1 of barite (weighting agent), 5% by weight of TF1 of binarysurfactant (as described above with reference to the control spacerfluid), 2% by weight of TF1 of synthetic paraffin (non-aqueous basefluid), and fresh water (aqueous base fluid) to balance. The secondoil-in-water emulsified spacer fluid (TF2) was prepared identically toTF1, except that it comprised 52.2% by weight of TF2 of barite(weighting agent) and 4% by weight of TF2 of synthetic paraffin(non-aqueous base fluid). The third oil-in-water emulsified spacer fluid(TF3) was also prepared identically to TF1, except that it comprised53.8% by weight of TF3 of barite (weighting agent) and 8% by weight ofTF3 of synthetic paraffin (non-aqueous base fluid). The slight variationin barite between the control spacer fluid, TF1, TF2, and TF3 was aresult of accommodating for the amounts of non-aqueous base fluid usedin the fluids. To separate beakers, 100 ml of the control spacer fluid,TF1, TF2, and TF3 were added for stability testing and observation.

The control spacer fluid and the experimental emulsified spacer fluidsTF1, TF2, and TF3 were visually observed for stability after 30 minutes.After 30 minutes, the control spacer fluid exhibited substantialsettling and inhomogeneity. However, none of TF1, TF2, or TF3 exhibitedany apparent settling and each remained a homogenous fluid.

The control spacer fluid and the experimental emulsified spacer fluidsTF1, TF2, and TF3 were thereafter visually observed for stability after60 minutes. After 60 minutes, the control spacer fluid exhibitedcontinued settling as compared to the 30 minute observation. And again,none of TF1, TF2, or TF3 exhibited any apparent settling and eachremained a homogeneous fluid.

The experimental emulsified spacer fluids TF1, TF2, and TF3 were finallyobserved after 48 hours and continued to remain stable fluids, with noapparent settling or inhomogeneity.

Example 2

In this example, the stability of conventional spacer fluids comprisingconventional surfactants as compared to the oil-in-water emulsifiedspacer fluids of the embodiments described herein was evaluated. A 14ppg non-emulsified control surfactant spacer fluid was preparedcomprising 52.2% by weight of the control spacer fluid of barite(weighting agent), 4% by weight of the control spacer fluid of syntheticparaffin (non-aqueous base fluid), 5% by weight of control spacer fluidof nonylphenol ethoxylate (surfactant), and fresh water (aqueous basefluid) to balance. An experimental 14 ppg oil-in-water emulsified spacerfluid (TF4) was prepared in accordance with the embodiments describedherein using 52.2% by weight of TF4 of barite (weighting agent), 5% byweight binary surfactant mixture (as described in Example 1), 4% byweight of TF4 of synthetic paraffin (non-aqueous base fluid), and freshwater (aqueous base fluid) to balance. To separate beakers, 100 ml ofthe control surfactant spacer fluid and TF4 were added for stabilitytesting and observation.

The control surfactant spacer fluid and the experimental emulsifiedspacer fluid TF4 were visually observed for stability after 30 minutes.After 30 minutes, the control surfactant spacer fluid exhibitedsubstantial settling and inhomogeneity. However, TF4 exhibited noapparent settling and remained a homogenous fluid.

The control surfactant spacer fluid and the experimental emulsifiedspacer fluid TF4 were thereafter visually observed for stability after60 minutes. After 60 minutes, the control surfactant spacer fluidexhibited continued settling as compared to the 30 minute observation.And again, TF4 exhibited no apparent settling and remained a homogenousfluid.

Therefore, the embodiments herein well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as theymay be modified and practiced in different but equivalent mannersapparent to those skilled in the art having the benefit of the teachingsherein. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. It is therefore evident that the particular illustrativeembodiments disclosed above may be altered, combined, or modified andall such variations are considered within the scope and spirit of thedisclosure. The embodiments illustratively disclosed herein suitably maybe practiced in the absence of any element that is not specificallydisclosed herein and/or any optional element disclosed herein. Whilecompositions and methods are described in terms of “comprising,”“containing,” or “including” various components or steps, thecompositions and methods can also “consist essentially of” or “consistof” the various components and steps. All numbers and ranges disclosedabove may vary by some amount. Whenever a numerical range with a lowerlimit and an upper limit is disclosed, any number and any included rangefalling within the range is specifically disclosed. In particular, everyrange of values (of the form, “from about a to about b,” or,equivalently, “from approximately a to b,” or, equivalently, “fromapproximately a-b”) disclosed herein is to be understood to set forthevery number and range encompassed within the broader range of values.Also, the terms in the claims have their plain, ordinary meaning unlessotherwise explicitly and clearly defined by the patentee. Moreover, theindefinite articles “a” or “an,” as used in the claims, are definedherein to mean one or more than one of the element that it introduces.If there is any conflict in the usages of a word or term in thisspecification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

The invention claimed is:
 1. A method comprising: providing an oil-in-water emulsified spacer fluid comprising a binary surfactant mixture, solvent non-aqueous base fluid, a weighting agent, and an aqueous base fluid, wherein the binary surfactant mixture comprises a surfactant and an amphiphilic co-surfactant in a ratio of surfactant to amphiphilic co-surfactant in the range of about 1:2 to 2:1, wherein the surfactant is a betaine and is present in an amount in the range of from about 0.5% to about 5% by weight of the oil-in-water emulsified spacer fluid and wherein the amphiphilic co-surfactant is present in an amount in the range of from about 0.5% to about 5% by weight of the oil-in-water emulsified spacer fluid, and wherein the amphiphilic co-surfactant is selected from the group consisting of an alcohol; an alkyl alcohol; an aliphatic alcohol; an alicyclic alcohol; an unsaturated aliphatic alcohol; an unsaturated alicyclic alcohol; a polyhydric alcohol; an aromatic alcohol; an ethoxylated alcohol; a propoxylated alcohol; a glycol; a glycol ether; a polyglycol amine; a phenol; an ethoxylated phenol; a propoxylated phenol; and any combination thereof; wherein the non-aqueous fluid is a paraffin and the non-aqueous fluid is present in an amount in the range of about 1% to about 10% by weight of the oil-in-water emulsified spacer fluid, wherein the weighting agent is in the amount of about 50% by weight to about 55% by weight of the oil-in-water emulsified spacer fluid, and introducing the oil-in-water emulsified spacer fluid into a subterranean formation comprising a residual non-aqueous fluid therein, wherein the binary surfactant mixture in the oil-in-water emulsified spacer fluid emulsifies at least a portion of the residual non-aqueous fluid; and wherein the combination of betaine and amphiphilic co-surfactant in a ratio of surfactant to amphiphilic co-surfactant in the range of about 1:2 to 2:1 together with paraffin in the amount of about 1% to about 10% by weight of the oil-in-water emulsified spacer fluid is able to produce an emulsion having low surfactant content which remains stable against settling for a period of time greater than about 48 hours.
 2. The method of claim 1, wherein the binary surfactant mixture increases the water wettability of the subterranean formation.
 3. The method of claim 1, wherein oil-in-water emulsified spacer fluid is a microemulsion comprising dispersed phase droplets having an average diameter in the range of from about 1 nm to about 100 nm.
 4. The method of claim 1, wherein the oil-in-water emulsified spacer fluid is a miniemulsion comprising dispersed phase droplets having an average diameter in the range of from about 50 nm to about 1 μm.
 5. The method of claim 1, wherein the oil-in-water emulsified spacer fluid is a macroemulsion comprising dispersed phase droplets having an average diameter in the range of from about 1 μm to about 100 μm.
 6. The method of claim 1, wherein the emulsified spacer fluid further comprises an additive selected from the group consisting of a salt; a weighting agent; an inert solid; a fluid loss control agent; an emulsifier; a dispersion aid; a corrosion inhibitor; an emulsion thinner; an emulsion thickener; a viscosifying agent; a gelling agent; a proppant; a lost circulation agent; a foaming agent; a gas; a pH control additive; a breaker; a biocide; a crosslinker; a stabilizer; a chelating agent; a scale inhibitor; a gas hydrate inhibitor; an oxidizer; a reducer; a friction reducer; a clay stabilizing agent; and any combination thereof.
 7. The method of claim 1 further comprising: removing the oil-in-water emulsified spacer fluid from the subterranean formation; introducing a casing string into the subterranean formation; introducing a cement composition into the subterranean formation so as to form a cement column in an annulus between the subterranean formation and the casing string; and setting the cement composition forming the cement column.
 8. The method of claim 7, wherein the aqueous base fluid in the oil-in-water emulsified spacer fluid is selected from the group consisting of fresh water; saltwater; brine; seawater; and any combination thereof.
 9. The method of claim 7, wherein the aqueous base fluid in the oil-in-water emulsified spacer fluid is present in an amount in a range of about 40% to about 70% by weight of the emulsified spacer fluid.
 10. The method of claim 7, wherein the amphiphilic co-surfactant is tertiary-butyl alcohol.
 11. The method of claim 7, wherein the emulsion is a microemulsion.
 12. A method comprising: providing an oil-in-water emulsified spacer fluid comprising a binary surfactant mixture, solvent non-aqueous base fluid, a weighting agent, and an aqueous base fluid, wherein the binary surfactant mixture comprises a surfactant and an amphiphilic co-surfactant in a ratio of surfactant to amphiphilic co-surfactant in the range of about 1:2 to 2:1, wherein the surfactant is a betaine present in an amount in the range of from about 0.5% to about 5% by weight of the oil-in-water emulsified spacer fluid, wherein the amphiphilic co-surfactant is tertiary-butyl alcohol present in an amount in the range of from about 0.5% to about 5% by weight of the oil-in-water emulsified spacer fluid, wherein the non-aqueous fluid is a paraffin and the non-aqueous fluid is present in an amount in the range of about 1% to about 10% by weight of the oil-in-water emulsified spacer fluid, wherein the weighting agent is in the amount of about 50% by weight to about 55% by weight of the oil-in-water emulsified spacer fluid, wherein the emulsified spacer fluid further comprises an additive selected from the group consisting of a salt; a weighting agent; an inert solid; a fluid loss control agent; an emulsifier; a dispersion aid; a corrosion inhibitor; an emulsion thinner; an emulsion thickener; a viscosifying agent; a gelling agent; a proppant; a lost circulation agent; a foaming agent; a gas; a pH control additive; a breaker; a biocide; a crosslinker; a stabilizer; a chelating agent; a scale inhibitor; a gas hydrate inhibitor; an oxidizer; a reducer; a friction reducer; a clay stabilizing agent; and any combination thereof, and introducing the oil-in-water emulsified spacer fluid into a subterranean formation comprising a residual non-aqueous fluid therein, wherein the binary surfactant mixture in the oil-in-water emulsified spacer fluid emulsifies at least a portion of the residual non-aqueous fluid; and wherein the combination of betaine and tertiary butyl alcohol in a ratio of surfactant to amphiphilic co-surfactant in the range of about 1:2 to 2:1 together with paraffin in the amount of about 1% to about 10% by weight of the oil-in-water emulsified spacer fluid is able to produce an emulsion having low surfactant content which remains stable against settling for a period of time greater than about 48 hours. 